Every heavy-rain season, a few Lower Mainland homeowners come downstairs to find sewage on the basement floor. It did not come from their plumbing. It came up through the lowest drain in the house because the municipal sewer in the street filled faster than it could empty. A backwater valve is the device that stops that.
What A Backwater Valve Does
It is a one-way gate installed in the building drain, downstream of the fixtures it protects. Waste flows out freely. If the sewer backs up, the flap closes and the surcharge cannot push back into the house. That is all it does, and on the night it matters it is worth more than anything else in the basement.
Who Needs One
- Any basement with a toilet, shower, laundry or floor drain below the level of the street sewer
- Homes in low-lying areas: Ladner, Queensborough, parts of Langley, Surrey and Richmond
- Older neighbourhoods on combined or undersized sewers
- Basement suites, where the fixtures are the lowest in the building
- Anyone who has had one backup already, because it will not be the last
Many Lower Mainland municipalities require a backwater valve on new suites and additions, and some offer a rebate for adding one to an existing home. We can tell you what applies at your address.
The Right Kind, In The Right Place
There are two common types. A normally-open valve sits open and only closes when flow reverses; it is the standard for a full building drain. A normally-closed valve is used on individual fixtures or branch lines. Putting the wrong type in the wrong place, or protecting the whole house when only the basement is below grade, causes venting and drainage problems of its own. Placement matters more than the part.
Installation
The building drain is exposed, usually by cutting the basement slab, and the valve is set in the line with an access cover flush to the floor so it can be inspected and cleaned. It needs a permit and an inspection in most municipalities. A camera inspection first confirms where the drain runs and what condition it is in, which avoids opening the floor in the wrong place.
Maintenance
Once or twice a year, lift the cover, check that the flap moves freely and that nothing is caught in it. A valve that is never looked at can seize open, which is the same as having no valve.
Related: sump pumps and battery backup · drainage and excavation
Related guides
- Tankless Water Heaters: Worth It In The Lower Mainland?
- Frozen Pipes: What To Do Right Now, And How To Prevent It
- Annual Boiler Service: What A Proper Visit Actually Covers
- Garburator Dos And Don’ts: What Actually Breaks Them
